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Brewer calibrations: what do they accomplish?

Brewer calibrations: what do they accomplish?. Volodya Savastiouk International Ozone Services Inc. Full Spectrum Science Inc. Presentation outline:. Why do Brewers need calibrations? What is done during calibrations? Recommended calibration frequency. Why do Brewers need calibrations?.

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Brewer calibrations: what do they accomplish?

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  1. Brewer calibrations: what do they accomplish? Volodya Savastiouk International Ozone Services Inc. Full Spectrum Science Inc. 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  2. Presentation outline: • Why do Brewers need calibrations? • What is done during calibrations? • Recommended calibration frequency. 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  3. Why do Brewers need calibrations? • The most important aspect of Brewer calibrations: maintaining the same ozone reference for all Brewers • The world’s reference for Brewers is the triad of Brewers in Toronto • Traveling reference Brewers with the triad either directly in Toronto or using traveling references #017 and #145 • Keeping the Brewers in working condition and fixing what’s broken • Measuring Brewer characterization parameters • Dead time, dispersion, UV response, ND filters • Optimal high voltage, SL power • Training and educating local personnel 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  4. Why do Brewers need calibrations? Remember how ozone is calculated in the Brewer software? X=(R6-ETC)/(a*mu) Measured CalEstablishedCalEstablished Calculated Extra Terrestrial Coefficients (ETC): Only a few Brewers are in locations that allow reliable absolute calibrations using the Langley extrapolation technique (Mauna Loa, Izana); the majority of instruments require comparisons with calibrated Brewers for establishing the ETC. Ozone absorption coefficient (a): established using the results of the dispersion test and the laboratory-measured ozone cross-sections. 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  5. What is done during calibrations? • Initial comparison with the traveling standard (if the Brewer is working) • Analysing available historical data • Collecting solar/sky data side-by-side with the standard • Applying the necessary corrections to the ozone calculations • Brewer inspection/maintenance • Tracker plate, micrometers, push rod, etc. • The extent of this is based on the history of the Brewer • Characterization tests • Dispersion, UV response, ND filters, dead time • Final comparison with the standard • Adjusting the ETC if needed 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  6. Data evolution Calibration • Data collection: • Observations • Tests • Notes (log-file) ETC SL ratio R6cal Run/Stop Dead Time Steps per revolution High voltage 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  7. Red marks indicate that the Run/Stop test was not ideal Overall, this instrument is working fine. Any individual test result does not necessarily describe the state of the instrument. Looking at the historical record is a much more reliable way to diagnose a Brewer. 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  8. A calibration visit and maintenance improved the RS results 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  9. o3 DEADTIME TEST AT 03:46:45, sep 08, 07 Deadtime (ns) for filter position 0 (high intensity) 3.787239E-08 (at 03:47:05) 3.875278E-08 (at 03:47:26) 3.93215E-08 (at 03:47:46) 3.742871E-08 (at 03:48:06) 3.821398E-08 (at 03:48:26) Mean = 38.317 Std Dev = .7 Deadtime (ns) for filter position 1 (low intensity) 3.635986E-08 (at 03:49:07) 3.64374E-08 (at 03:49:27) 3.58004E-08 (at 03:49:47) 3.638064E-08 (at 03:50:07) 3.434979E-08 (at 03:50:27) 3.624829E-08 (at 03:50:47) 3.821146E-08 (at 03:51:07) 4.033888E-08 (at 03:51:27) 3.89437E-08 (at 03:51:47) 3.515724E-08 (at 03:52:07) Mean = 36.822 Std Dev = 1.8 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  10. Dead time slowly changed from 34 nsto 32 ns 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  11. Look for sudden changes in the SL test results 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  12. A/D Values for sep 09/07 at 00:24:56 for instrument number ### Channel# Name Value Value (Lamps off) (Lamps on) 0 Brewer temp 1 (deg C) 23.75 22.81 1 Brewer temp 2 (deg C) -10.94 -10.94 2 Brewer temp 3 (deg C) 21.88 21.88 3 H.T. voltage (V) 1446.46 1446.46 4 +15V power supply (V) 14.87 14.87 5 + 5V power supply (V) 5.03 5.00 6 -15V power supply (V) -15.05 -15.05 7 +24V power supply (V) 23.40 23.75 8 Rate meter (kc/s) 0.00 15.60 9 Not used (bits) 0.00 0.00 10 Not used (bits) 0.00 0.00 11 Not used (bits) 0.00 0.00 12 + 5V ss (V) 4.95 4.95 13 - 8V ss (V) -8.11 -8.15 14 Std lmp current (A) 0.07 1.68 15 Std lmp voltage (V) 0.00 10.23 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  13. Sun scan test – final wavelength setting for the Brewer Cal.step 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  14. Data evolution Calibration DS ozone observations SL tests ETC SL ratio R6cal Real-time ozone values SL-corrected ozone values Calibration ETC*=ETC+(R6-R6cal) ETC SL ratio R6cal 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  15. Data evolution When to do maintenance to preserve calibration history? Calibration Observation Calibration Calibration Observation 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  16. Recommended calibration frequency This is a difficult one. From our experience, a calibration every two years is enough for most Brewers. However, we definitely see the most stability with Brewers that are visited every year. Historical data are often a good indicator on whether the Brewer may benefit from annual calibrations. Of course, all of this is based on the assumption that regular normal maintenance is done to the Brewer between the calibration visits, but that’ll be the topic of another talk. 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  17. Conclusions: In order to maintain (and improve) the quality of the Brewer ozone data regular calibration and maintenance visits are required. It is extremely important to keep the Brewer network traceable the the main Brewer reference, the triad. 13th Brewer User Workshop. Beijing, China September 12-16, 2011

  18. Thank you! Eureka, Canada, February 2011 13th Brewer User Workshop. Beijing, China September 12-16, 2011

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